The present invention relates to medical instrumentation, and more particularly, to a system for measuring the core temperature of the human body by detecting and analyzing infrared emissions in the external ear canal of a patient.
The diagnosis and treatment of many body ailments depends upon an accurate reading of the internal or core temperature of a patient's body, and in some instances, upon a comparison to a previous body temperature reading. For many years, the most common way of taking a patient's temperature involved the utilization of a Mercury thermometer. This approach has a number of drawbacks. First of all, such thermometers are normally made of glass. They must be inserted and maintained in the patient's mouth or rectum for several minutes. This is often discomforting to the patient. Furthermore, such thermometers can break, resulting in serious lacerations or mercury poisoning. In addition, Mercury thermometers are difficult to read, must be sterilized, and must be "shaken down" vigorously to place the Mercury at the bottom end prior to use.
Because of the above drawbacks of conventional Mercury thermometers, electronic thermometers were developed and are now in widespread use. Typically, such electronic thermometers have a probe connected by wires to a remote unit containing an electronic circuit. The probe is sheathed in a protective, disposable cover before being inserted into the patient's mouth or rectum. Using predictive techniques, the patient's temperature reading is taken in a significantly shorter time period, for example thirty seconds, compared to the several minutes required for conventional Mercury thermometers. Such electronic thermometers normally have meters or other displays which enable the operator to determine the temperature much more readily than reading the position of the terminal end of a column of Mercury in a glass tube. Also, the electronic thermometers in some instances provide more accurate temperature readings than Mercury thermometers. Furthermore, the protective sleeves are disposable, thus allowing the same thermometer to be used over and over without autoclaving or other sterilization.
The tympanic membrane is generally considered by the medical community to be superior to oral, rectal or axillary sites for taking a patient's temperature. This is because the tympanic membrane is more representative of the body's internal or core temperature and more responsive to changes in the core temperature. Heretofore, efforts to provide a method and apparatus for measuring the body temperature via the external ear canal have not been successful. U.S. Pat. No. 3,282,106 of Barnes suggests the concept of an infrared thermometer that may be placed in the ear cavity to measure body temperature.
Infrared sensing devices have been commercially available for measuring the skin temperature of a patient. However, a patient's skin temperature varies over a much wider range than his or her internal body temperature and is not generally used by physicians in the diagnosis and treatment of illnesses. Furthermore, these devices are large and cumbersome and not suited for detecting infrared emissions in the external ear canal.
U.S. Pat. No. 3,581,570 discloses a tympanic temperature sensing device which has positioning means to establish a fixed relationship between the eardrum and a radiometer. The radiometer is a thermister, bolometer or thermocouple. The circuit consists of merely an amplifier and a calibrated galvanometer. A polyethylene shield fits over the probe portion to protect the radiometer.
Attempts have also been made to determine a patient's body temperature via the external ear canal using devices other than infrared sensors. For example, U.S. Pat. No. 3,054,397 discloses the concept of inserting a thermoelectric probe which may contain a thermocouple or a thermistor into the ear until it touches the tissues, for example the eardrum. This type of measurement is not practical for every day hospital or clinical use because of danger of injury to the eardrum. It also may expose the patient to considerable anxiety if not pain.
U.S. Pat. No. 3,491,596 discloses the concept of placing a probe containing a field effect transistor into the ear canal to measure the radiated energy. In one embodiment, a heater element is used to preheat the field effect transistor to the approximate temperature to be sensed to reduce the response time.
U.S. Pat. No. 3,626,757 describes an ear thermometer which contains a probe which must make contact with the tympanum. This device is too invasive and slow in response for routine hospital use.
U.S. Pat. No. 4,191,197 discloses a touch free tympanic thermometer in which heated air having a temperature value close to body temperature is blown against the eardrum. The actual body temperature is determined by measuring the temperature of the returning air. Clearly, this device would have serious accuracy limitations.
Another tympanic thermometer which s commercially available is the MON-A-THERM Model 6000. It uses a thermocouple as the sensing transducer. Contact with the tympanic membrane is required which is painful and potentially hazardous to the patient. The device also requires two to three minutes to arrive at the temperature.